Although improved testing methods for hepatitis B (HBV), hepatitis C (HCV), and human immunodeficiency virus (HIV) have markedly reduced the incidence of transfusion associated diseases, other viral, bacterial, and protozoal agents are not routinely tested for, and remain a potential threat to transfusion safety. Schmunis, G. A., Transfusion 31:547-557 (1992). In addition, testing will not insure the safety of the blood supply against future unknown pathogens that may enter the donor population resulting in transfusion associated transmission before sensitive tests can be implemented.
The recent introduction of a blood test for HCV will reduce transmission of this virus; however, it has a sensitivity of only 67% for detection of probable infectious blood units. HCV is responsible for 90% of transfusion associated hepatitis. Melniek, J. L., Abstracts of Virological Safety Aspects of Plasma, Cannes, November 3-6 (1992) page 9. It is estimated that, with the test in place, the risk of infection is 1 out of 3300 units transfused.
Further, while more sensitive serological assays are in place for HIV-1 and HBV, these agents can nonetheless be transmitted by seronegative blood donors. International Forum: Vox Sang 32:346 (1977). Ward, J. W., et al., N. Engl. J. Med., 318:473 (1988). Up to 10% of total transfusion-related hepatitis and 25% of severe icteric cases are due to the HBV transmitted by hepatitis B surface antigen (HBasAg) negative donors. Vox Sang 32:346 (1977). To date, fifteen cases of transfusion-associated HIV infections have been reported by the Center for Disease Control (CDC) among recipients of blood pretested negative for antibody to HIV-1.
Even if seroconversion tests were a sufficient screen, they may not be practical in application. For example, CMV (a herpes virus) and parvo B19 virus in humans are common. When they occur in healthy, immunocompetent adults, they nearly always result in asymptomatic seroconversion. Because such a large part of the population is seropositive, exclusion of positive units would result in substantial limitation of the blood supply.
An alternative approach to eliminate transmission of viral diseases through blood products is to develop a means to inactivate pathogens in transfusion products. Development of an effective technology to inactivate infectious pathogens in blood products offers the potential to improve the safety of the blood supply, and perhaps to slow the introduction of new tests, such as the HIV-2 test, for low frequency pathogens. Ultimately, decontamination technology could significantly reduce the cost of blood products and increase the availability of scarce blood products. Furthermore, decontamination may extend the storage life of platelet concentrates which, according to Goldman M. and M. A. Blajchman, Transfusion Medicine Reviews. V: 73-83 (1991), are currently limited by potential bacterial contamination.
Several methods have been reported for the inactivation or elimination of viral agents in erythrocyte-free blood products. Some of these techniques, such as heat (Hilfenhous, J., et al., J. Biol. Std. 70:589 (1987)), solvent/detergent treatment (Horowitz, B., et al, Transfusion 25:516 (1985)), gamma-irradiation (Moroff, G., et al., Transfusion 26:453 (1986)), UV radiation combined with beta propriolactone, (Prince A. M., et al., Reviews of Infect Diseases 5:92-107 (1983) Prince A. M., et al., Reviews of Infect Diseases 5:92-107 (1983)), visible laser light in combination with hematoporphyrins (Matthews J. L., et al., Transfusion 28:81-83 (1988); North J., et al., Transfusion 32:121-128 (1992)), use of the photoactive dyes aluminum phthalocyananine and merocyanine 540 (Sieber F., et al., Blood 73:345-350 (1989); Rywkin S., et al., Blood 78 (Suppl 1):352a (Abstract) (1991)) or UV alone (Proudouz, K. N., et al., Blood 70:589 (1987)) are completely incompatible with maintenance of platelet function.
Other methods inactivate viral agents by using known furocoumarins, such as psoralens, in the presence of ultra-violet light. Psoralens are tricyclic compounds formed by the linear fusion of a furan ring with a coumarin. Psoralens can intercalate between the base pairs of double-stranded nucleic acids, forming covalent adducts to pyrimidine bases upon absorption of long wave ultraviolet light (UVA). G. D. Cimino et al., Ann. Rev. Biochem. 54:1151 (1985); Hearst et al., Quart. Rev. Biophys. 17:1 (1984). If there is a second pyrimidine adjacent to a psoralen-pyrimidine monoadduct and on the opposite strand, absorption of a second photon can lead to formation of a diadduct which functions as an interstrand crosslink. S. T. Isaacs et al., Biochemistry 16:1058 (1977); S. T. Isaacs et al., Trends in Photobiology (Plenum) pp. 279-294 (1982); J. Tessman et al., Biochem. 24:1669 (1985); Hearst et al., U.S. Pat. Nos. 4,124,598, 4,169,204, and 4,196,281, hereby incorporated by reference.
The covalently bonded psoralens act as inhibitors of DNA replication and thus have the potential to stop the replication process. Due to this DNA binding capability, psoralens are of particular interest in relation to solving the problems of creating and maintaining a safe blood supply. Some known psoralens have been shown to inactivate viruses in some blood products. H. J. Alter et al., The Lancet (ii:1446) (1988); L. Lin et al., Blood 74:517 (1989) (decontaminating platelet concentrates); G. P. Wiesehahn et al., U.S. Pat. Nos. 4,727,027 and 4,748,120, hereby incorporated by reference, describe the use of a combination of 8-methoxypsoralen (8-MOP) and irradiation. P. Morel et al., Blood Cells 18:27 (1992) show that 300 ug/mL of 8-MOP together with ten hours of irradiation with ultraviolet light can effectively inactivate viruses in human serum. Similar studies using 8-MOP and aminomethyltrimethylpsoralen (AMT) have been reported by other investigators. Dodd RY, et al., Transfusion 31:483-490 (1991); Margolis-Nunno, H., et al., Thromb Haemostas 65:1162 (Abstract) (1991). Indeed, the photoinactivation of a broad spectrum of microorganisms has been established, including HBV, HCV, and HIV. [Hanson C. V., Blood Cells: 18:7-24 (1992); Alter, H. J., et al., The Lancet ii:1446 (1988); Margolis-Nunno H. et al., Thromb Haemostas 65:1162 (Abstract) (1991).]
Psoralen photoinactivation is only feasible if the ability of the psoralen to inactivate viruses is sufficient to ensure a safety margin in which complete inactivation will occur. On the other hand, the psoralen must not be such that it will cause damage to blood cells. Previous compounds and protocols have necessitated the removal of molecular oxygen from the reaction before exposure to light, to prevent damage to blood products from oxygen radicals produced during irradiation. See L. Lin et al., Blood 74:517 (1989); U.S. Pat. No. 4,727,027, to Wiesehahn. This is a costly and time consuming procedure.
Finally, some commonly known compounds used in PCD cause undesirable mutagenic effects which appears to increase with increased ability to kill virus. In other words, the more effective the known compounds are at inactivating viruses, the more mutagenic the compounds are, and thus, the less useful they at any point in an inactivation system of products for in vivo use. A new psoralen compound is needed which displays improved ability to inactivate pathogens and low mutagenicity, thereby ensuring safe and complete inactivation of pathogens in blood decontamination methods.